The use of L-ascorbic acid as an anti-oxidant in food preparations is known. For example, Steinhart, Pro- and Antioxidative Effect of Ascorbic Acid on L-Tryptophan in the System Fe.sup.3+ /Ascorbic Acid/O.sub.2, J. Agric. Food Chem., Vol. 41, pages 2275-2277 (1993) describes the use of L-ascorbic acid as an anti-oxidant which performs its function in food by removing free radicals and undergoing rapid oxidation itself.
Similarly, free L-ascorbic acid in topical preparations demonstrates poor stability and tends to break down due to partially oxidative and non-oxidative degradation. The degraded ascorbic acid loses activity and the host product loses aesthetic appeal by exhibiting a brown color which is unacceptable for commercial cosmetics.
U.S. Pat. No. 4,939,128 describes an ingestible ascorbic acid conjugated with different hydrocarbon groups through a phosphate linkage. These compounds are indicated for use as an oral therapeutic for treating ischemic injury to cell tissue of internal organs. The '128 patent specification does not indicate a need for storage stability nor a need for maintaining aesthetic appearances of the disclosed compounds such as required in topical cosmetics.
Attempts have been made to use ascorbic acid conjugated with a glycyrrhetic group as described in European Application No. 92104149.7; and with a tocopheryl group as indicated by U.S. Pat. No. 3,151,127. U.S. Pat. Nos. 4,564,686 and 5,306,713 also disclose tocopheryl ascorbyl phosphate as an anti-oxidant having the following structure. ##STR2##
Sakamoto, Measurement Method of Efficacy of Antidandruff Cosmetics and Development of the New Active Commercial Product, IFSCC, Yokohama, Vol. B206, pages 823-864 (1993) describes the use of tocopheryl coupled to L-ascorbic acid. The coupled tocopheryl is an anti-oxidant preservative for the ascorbyl group. None of these teachings provide a method of using a stable, ascorbic acid derivatized with a straight chain alkyl group as a topical agent.
There is a need in the art for a method of using an ascorbic acid derivative having a phosphate linked straight chain alkyl group for improving skin condition and appearance wherein the ascorbic acid is stable, has a long shelf-life and is bioavailable upon topical application even after long term storage.